High frequency test device

ABSTRACT

A high frequency signal generator and calibrated radiator system for providing signals for testing the tracking response of a radar receiver system simulates an apparent target rapidly movable along a line substantially at right angles to the direction of the system under test.

O United States Patent [1 1 3,683,381

Strenglein 1 Aug. 8, 1972 [54] HIGH FREQUENCY TEST DEVICE 3,214,75810/1965 Mills et a]. ..343/17.7 [72] Inventor: Harry E strenglein,Clearwater, 3,229,289 l/l966 Stine ..343/]7.7

a Primary ExaminerT. H. Tubbesing [73] Assignee: Sperry Rand CorporationAttorney-S. C. Yeaton 'l F b. 1 l [22] F1 ed e 971 ABSTRACT I A l. N l 1PP 0 L393 A high frequency Signal generator and calibrated radiatorsystem for providing signals for testing the [52] US. Cl ..343/l7.7,35/lO.4 tracking response of a radar receiver system simulates [51] anapparent target rapidly movable along a line sub- [58] Field of Search..343/l7.7; 35/l().4 stantially at right angles to the direction of thesystem under test.

[56] References Cited 7 Claims, 3 Drawing Figures UNITED STATES PATENTS3,164,835 1/1965 Alsberg ..343/17.7 X

POWER HYBRID DIVIDER NETWORK 13m, 14 L A 15 BALANCED MODULATOR CONTROLPAIENTEDMI 1912 3.553381 sumlurz PRIOR ART 5 SWITCH q/2 HIGH FREQUENCY'3 SOURCE SWITCH 7a CONTROL S 10 5 FIG 2 I/VVE/VTOR HARRY F STRENGLE/N ATTOHNEY PATENTED 8 1973 3,683,381

SHEET 2 BF 2.

CONTROL I/VVE/VTOR HARRY F STREA/GLE/A/ A TTOR/VE) BACKGROUND OF THEINVENTION 1. Field of the Invention The invention pertains to the art ofmeasurement of the tracking response of radar receiver systems and moreparticularly relates to means for generating signals permittingmeasurement of the behavior of rapid response monopulse tracking radarreceiver devices.

2. Description of the Prior Art Prior art techniques for testing thetracking response of radar receivers to an apparent moving target havenot proven adequate for investigation of the characteristics of modernhighly sensitive tracking radar receivers. For investigation of oldertypes of receivers, the apparent target has sometimes been simulated bygross mechanical movement of an element of an excited test antenna sothat the apparent target position moves along a line generallyperpendicular to the direction to the radar device under test. At othertimes, physical switching of the excitation between first and secondtest antennas has been employed. In testing modern receivers that usemonopulse techniques, calibrated, repeatable rates of change of theapparent target position of the order of a degree per microsecond arerequired. Such a requirement cannot be satisfactorily approached by theprior art methods or apparatus, as will be further explained.

SUMMARY OF THE INVENTION The present invention relates to a calibratedhigh frequency signal generation and radiation system for providingsignals for the testing of the angular tracking response of sensitivemonopulse tracking radar apparatus. The test signal generator systemsimulates a target movable rapidly in a predetermined manner along aline substantially at right angles to the direction of the monopulsereceiver being tested.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphical diagram usefulin explaining the problem solved by the invention.

FIG. 2 is a block diagram showing the connections of electricalcomponents of a prior art signal generator.

FIG. 3 is a block diagram showing the electrical components and theirconnections in a preferred form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, it isdesired according to the present invention to test the characteristicsof a monopulse radar target tracking receiver system by moving theapparent location of a simulated target at a rapid but controlled rate.For testing monopulse receivers, it is desired to move the apparenttarget at a rate much greater than is possible by mechanical means. Itis also desired to use means accurately repeatable and calibratable,especially as to the zero or null position of the apparent target. Forexample, assume that the circle C in FIG. 1 represents the locus of amonopulse device whose response is to be examined and that circle C lieson a reference axis OX, to which line AOB is substantiallyperpendicular. According to the requirements for making meaningful testsof the monopulse devices, it must be possible to move an apparent targetalong the substantially perpendicular line AOB at a predetermined rapidrate and to know accurately the location of the origin 0. For example,these requirements apply to the rapid motion of an apparent targetlocated instantaneously at point B and radiating an antenna pattern Tsymmetrically located with respect to an axis BD while illuminating amonopulse device at location C. In effect, it is desired to vary theangle 0 between axes OX and BD rapidly and in a bipolar sense about itszero value.

Prior art electrical test systems for producing apparent target motiondo not fit the needs of equipment satisfactory for testing monopulsedevices. For example, FIG. 2 illustrates a prior art system consistingof spaced antennas 1 and la that are usually directional and fedco-phasally with high frequency energy propagated into the antennas bytee junction 3. The third port of tee 3 is supplied with high frequencyenergy by the pulsed high frequency source 4. Between antenna l and tee3 is interposed a switch or attenuator 2; similarly, between antenna laand tee 3, there is interposed a second switch or attenuator 2a. Devices2 and 2a are operated according to reciprocal output signals of control5, which may be a manual or automatically operated device. Devices 2, 2amay be electrically variable attenuators of a well known type, or may besemiconductor diode switching devices. The drive signals suppliedrespectively by leads 7, 7a to switches 2, 2a operate in a reciprocalmanner; i.e., when the signal on lead 7 causes switch 2 to conduct, thaton lead 7a places switch 2a in its non-conducting state and vice versa.In use, the device of FIG. 2 would be located at the origin 0 in FIG. 1.

Whether attenuators or switches are employed in the prior art system ofFIG. 2, certain problems arise. At the time that the apparent targetshould be at its null position (angle 0 in FIG. 1 is then zero), theattenuators or switches should have equal insertion phasecharacteristics and minimum insertion losses so that equal power is fedco-phasally to each antenna 1, la. At this point, any phase or amplitudeasymmetry in the switches or attenuators results in a correspondingunbalance in the power delivered to antennas 1, 1a. This, in turn,yields an erroneous indication of the apparent target position as seenby the monopulse device under test.

If high frequency switches employing diodes are used, the diodesselected are usually p-i-n diodes. However, even these diodes switchrapidly only when considerably overdriven. When used as linear controldevices, they have comparatively slow and non-linear response. Also, theresponse is not desirably repeatable because of the charge carrier lifetime characteristics of such semiconductor devices.

According to the embodiment of the invention shown in FIG. 3, thedifficulties of the prior art are overcome. The device of FIG. 3 wouldbe placed at the origin 0 of FIG. 1 and employs a pair of spacedantennas 17 and 17a directed in parallel relation toward the monopulsedevice to be tested. Antennas 17 and 17a are respectively fed fromsymmetric ports of hybrid network 16, which latter may be a conventionalhybrid junction of the magic tee type.

For exciting antennas 17, 17a, pulsed high frequency or microwave energyis fed by source to an input port of the equal power divider 1 l, whichlatter may be a simple tee junction or a 3 dB hybrid network. Half ofthe input power is fed directly by transmission line 12 to the sum port2 of hybrid network 16. The other half of the power supplied by divider11 is fed by transmission line 13 to a conventional high frequencymicrowave balanced modulator whose output port is connected bytransmission line 14 to the difference port A of hybrid network 16.Balanced modulator 15 is of the electronically controllable type, sothat a voltage analogous to the desired apparent target position may beintroduced into it on electrical lead 19, such as a repeating triangularvoltage wave 18a. The control voltage on lead 19 may be manually orautomatically generated by control or function generator 18. Theeffective transmission line lengths of line 12 and of the line composedof lines 13 and 14 and modulator 15 are so arranged that the output ofmodulator 15 when driven by its maximum control voltage appears at oneantenna in phase with the sum port 2 signal and at the other port inphase opposition. The respective transmission lines between hybridnetwork 16 and antennas 17 and 17a have equal lengths. Fixed attenuationmay be placed in transmission line 12 or an unequal power divider may beused in place of equal power divider 11 to compensate for the insertionloss of balanced modulator 15. However, the refinement is not essential,because the absence of such compensation merely alters the achievablerange of apparent target motion and does not affect the null position orthe calibration of the device.

According to one manner of operation of the invention, when the controlsignal supplied by control 18 to the balanced amplitude modulator 15 isat its zero level, the output of modulator 15 is substantially zero.Then, all of the power supplied by source 10 is fed to hybrid network 16via the sum port 2. Since equal power is then fed to antennas l7 and17a, the apparent source of the radiated energy is at the center of thearray (half way between antennas l7 and 17a), which center is understoodto be located at the origin 0 of FIG. 1. Thus the pair of antennas 17and 17a form an antenna array having 3 dB more gain than either of theindividual antennas.

When the triangular or other control voltage fed by lead 19 to balancedmodulator 15 reaches one of its two extreme values, equal halves of thepower are fed to the respective sum and difference ports 2 and A ofnetwork 16. Because of the inherent well known phase modifyingcharacteristics of network 16, all power is then fed by network 16 toonly one of the antennas 17, 17a, none emanating from the other antenna.The apparent target position then coincides with the position of theantenna having maximum output. The total effective radiated powerremains the same as indicated in the condition discussed in thepreceding paragraph.

When the control voltage fed by lead 19 to balanced modulator 15 reachesthe second of its two extreme values, equal halves of the power are fedagain to the respective sum and difference ports 2 and A of network 16,but now with a relative 180 phase difference. Consequently, the antennaat which maximum power was present in the condition of the immediatelypreceding paragraph no longer radiates and the antenna that previouslyradiated no power radiates maximum power, the apparent target positionbeing shifted to it. intermediate conditions of modulator 15 cause theapparent source to be located at a corresponding position lying betweenantennas 17, 17a.

The use of a balanced modulator such as device 15 in only one arm of thesystem has important consequences. When modulator 15 is in its zerooutput condition, not only is equal power delivered to both antennas 17,17a, but the sum of the powers delivered to antennas 17, 17a is half ofthe available power. When the power is delivered to a single one of thetwo antennas, all of the power is delivered. The importantcharacteristic of the combination including the single balancedmodulator 16 is that it matches the characteristic of the antenna arrayso that constant power is radiated toward the device under test for anycondition of balanced modulator 15. Further, the antennas 17, 17a remainproperly isolated and the location of and symmetry about the zero ornull position of the apparent target are readily assured.

The broad band, balanced modulator 15 is a desirable control device,since the amplitude of its high frequency output is linearlyproportional to the modulating voltage appearing on lead 19, permittinglinear motion of the apparent target location. Further, unlike the priorart diode switching device, it does not use semiconductor devices suchas p-i-n diodes and the consequent large and variable delay between theswitch drive voltage and the state of the corresponding output highfrequency amplitude is eliminated.

While the apparatus involved in observing or recording the perfection ofangular response of the monopulse device under test is not a necessarypart of this invention, it will be apparent to those skilled in themonopulse radar art and in the servomechanisms art that a direct measureof the angular sensing response of the monopulse device may readily becompared as to relative phase and amplitude with the voltage appearingupon control lead 19. Lag of the response and other peculiarities of thesystem under test may be analyzed, for instance, according to themethods conventionally used with prior art test apparatus such as thatof FIG. 1. It will be apparent to those skilled in the art that thenovel apparatus is equally useful with monopulse and other types ofangular tracking radar systems.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than of limitation and that changes within thepurview of the appended claims may be made without departure from thetrue scope and spirit of the invention in its broader aspects.

1 claim:

1. Signal generator apparatus for generating signals permitting testingof the angular response of an angular tracking receiver comprising:

signal source means having output means,

power divider means connected to said output means and having first andsecond port means,

hybrid network means having sum port means, difference port means, andthird and fourth port means,

first and second antenna means respectively connected to said third andfourth port means and comprising antenna array means adapted for spacepropagation of said signals from an effective radiation center adjacentsaid array means, first transmission line means connecting said firstport means and said sum port means, I

second transmission line means connecting said second port means andsaid difference port means, and

modulator means connected in one of said transmission line meansoperable to cause adjustable shifting of said effective radiation centeralong said array means.

2. Apparatus as described in claim 1 wherein said modulator meanscomprises balanced amplitude modulator means.

3. Apparatus as described in claim 2 comprising function generator meansfor controlling the state of said balanced modulator means.

4. Apparatus as described in claim 3 wherein said signal source means,said power divider means, said antenna array means, said transmissionline means, said balanced modulator means, and said function generatormeans are so constructed and arranged as to afford substantiallyconstant power radiation independent of the location of said efi'ectiveradiation center along said array means.

5. Apparatus as described in claim 4 wherein said power divider meanssubstantially equally divides power between said first and second portmeans.

6. Apparatus as described in claim 5 wherein said modulator means islocated in said second transmission line means.

7. Apparatus as described in claim 6 wherein said function generatormeans comprises a generator of triangular waves.

1. Signal generator apparatus for generating signals permitting testingof the angular response of an angular tracking receiver comprising:signal source means having output means, power divider means connectedto said output means and having first and second port means, hybridnetwork means having sum port means, difference port means, and thirdand fourth port means, first and second antenna means respectivelyconnected to said third and fourth port means and comprising antennaarray means adapted for space propagation of said signals from aneffective radiation center adjacent said array means, first transmissionline means connecting said first port means and said sum port means,second transmission line means connecting said second port means andsaid difference port means, and modulator means connected in one of saidtransmission line means operable to cause adjustable shifting of saideffective radiation center along said array means.
 2. Apparatus asdescribed in claim 1 wherein said modulator means comprises balancedamplitude modulator means.
 3. Apparatus as described in claim 2comprising function generator means for controlling the state of saidbalanced modulator means.
 4. Apparatus as described in claim 3 whereinsaid signal source means, said power divider means, said antenna arraymeans, said transmission line means, said balanced modulator means, andsaid function generator means are so constructed and arranged as toafford substantially constant power radiation independent of thelocation of said effective radiation center along said array means. 5.Apparatus as described in claim 4 wherein said power divider meanssubstantially equally divides power between said first and second portmeans.
 6. Apparatus as described in claim 5 wherein said modulator meansis located in said second transmission line means.
 7. Apparatus asdescribed in claim 6 wherein said function generator means comprises agenerator of triangular waves.